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Colorado forecaster: Avalanches abound this season

Avalanche forecaster Scott Toepfer talks danger, avy science

By Sarah Kuta kuta@coloradodaily.com

Posted:
01/09/2013 08:24:23 PM MST

Updated:
01/09/2013 08:32:11 PM MST

With snow in the forecast for the San Juan Mountains Thursday night and the rest of Colorado on Friday, we checked in with Colorado Avalanche Information Center's Scott Toepfer to talk snowslides, avalanche science and what to expect this season.

So, what's the deal with avalanches and snow in Colorado this winter?

Avalanches are somewhat cyclical. They tend to play off what storm cycles are doing. We went through a pretty good storm cycle the last half of December and into the first few days of January. Of course, the avalanche danger spiked upwards quite a bit.

We've had an avalanche warning out for a few of the zones around Colorado since then. This has to do with the time of year as well. We've got long nights and they've been quite cold up in the mountains, but not much new snow and the winds haven't been too bad.

So the avalanche danger has been decreasing, but those long cold nights are setting us up for a potential problem with this next incoming storm cycle set to arrive Friday or Saturday.

Can you explain why long, cold nights are bad for folks who like to play in the backcountry?

What those cold clear nights have done with the snow that's on the ground--it's become structurally very, very weak.

When there's old snow on the ground and it's shallow like it is this year, there develops a very large change in temperature between the ground and the surface of the snow. These large temperature changes turn the snow on the ground into a very sugary, granular snow grain. That square-ish, sugar-ish snow becomes very structurally weak. In other words, it doesn't accept much load.

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The ground is warm, in general, it's right about 32 degrees Fahrenheit. If the snowpack is shallow, the surface of the snow this time of year, we've had a lot of night time temperatures where it's been -10, -15, -30. That's a huge temperature gradient. That makes the snow pack change to a sugary form very quickly.

The snow becomes very square-ish in shape and those squares don't bond together very well. It's a very unstable structure.

What's a good way to think of how this sugary, granular snow causes avalanches?

It's like, you build your house on a foundation of potato chips. You might do OK getting up through the sub-floor, but as soon as you start putting up walls and the second floor, the third floor, the roof, your kitchen appliances, your furniture -- those potato chips cannot support that additional load, especially if it comes in fast. It rapidly stresses the snow pack.

You've got six kids and you have to get them off to school and none of them has done their homework. It adds to the stress of the whole equation in the morning. And that's what happens. Long, cold nights weaken the snow pack on the ground, if that snow pack is shallow. If the snow pack is deep, a meter or two meters, it's not so much a problem.

Are these conditions common for Colorado?

It's nothing unusual for us. There are some things (that are new). We had a lot of snow in December. a place like Steamboat -- it was their sixth snowiest December on record up there. But that still doesn't mean there's much snow on the ground and (the snow we do have) is very dry and light, there are a lot of spaces between the grains.

There's a lot more of this weak snow on the ground than we have seen in a number of years which means we're going to see bigger and more avalanches than we've seen in the past and the danger is going to linger longer.

Can you talk about some of the challenges of forecasting avalanche danger?

We can get a good handle on what the avalanche conditions are going to be by looking at the weather and the old snow on the ground -- all the scientific principles.

The thing that's harder to get a grasp on is how humans behave. In Colorado, people like to go out and recreate in the winter snow and this is all well and good, I do it every chance I can. But some people are going to be greater risk takers than others. Some people are going to have this mindset that bad things happen to other people, they don't happen to me.

Other people just don't know anything about avalanches. They go out because they just moved to Colorado from Miami. You've got all these people out there with different thought processes, different levels of education, different goals. It's much more difficult to forecast.

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So, can you give us a timeline for when it might be safe, or at least safer, to play in the backcountry? (Laughing) I'm one of those people who've been around for a long time, and I've had a lot of friends die in avalanches. It's pretty easy for me to rein it in. This year, to me, has a lot of similarities to last year and those similarities are not good ones.

I just feel that in our snow climate here in Colorado, nine out of 10 years the snowpack is really dangerous. One out of 10 years is a good snowpack, but this is one of those nine. I hate being that Chicken Little, (saying) that the sky is falling, the sky is falling, but I also look at what my peers are seeing and what I am seeing. So I don't see us getting out of the woods anytime soon. They have a lot of snow up in Canada where it might be a little bit safer.

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